1. Field of the Invention
The present invention relates to antenna systems, and, more particularly, to feedhorns for use with antenna systems.
2. Description of the Related Art
A feedhorn or "feed" is a device located at the focus point of a parabolic antenna that acts as a receiver or transmitter of radio wave or microwave frequency energy. Transmitted signals and received signals are at different frequencies to prevent interference. When acting as a receiver, the antenna collects, focuses, and couples the radio wave or microwave energy to the feedhorn, which in turn is coupled with transmission lines and an amplifier. Feedhorns are usually located outdoors, where ice or moisture may collect in the receiving end of the feedhorn, attenuating radio or microwave frequency energy entering or exiting the feedhorn.
It is known to pressurize the inside of a feedhorn with dry air and seal it with a mylar window covering the wide end of the feedhorn. The sealed, dry air prevents the formation of ice or liquid water on the inside of the feedhorn. However, a problem with this method is the difficulty in achieving and maintaining the seal. The seal may leak initially, or it may deteriorate with wear and age. Another problem is that dew, frost or ice may still form on the outside of the mylar window, blocking radio or microwave frequency energy from entering the feedhorn. Yet another problem is that liquid water does not quickly evaporate on a cold surface, so water, in addition to ice, may also collect and attenuate energy which enters or exits the feedhorn.
It is also known to place a heater assembly around the wide end of a feedhorn of an antenna to melt and prevent the formation of ice, snow or water on the feedhorn. For example, U.S. patent application Ser. No. 08/832,527, entitled SATELLITE FEEDHORN INCLUDING HEATER ASSEMBLY, now allowed (U.S. Pat. No. 5,844,528) and assigned to the assignee of the present invention, discloses an elongate element in the form of a cable tie which may be attached to the end of a feedhorn in an antenna system. A heater wire is wrapped around the cable tie and connected with a source of electrical power. The heater assembly effectively reduces or eliminates the accumulation of ice, water or snow on the feedhorn.
The heater assembly as described in U.S. patent application Ser. No. 08/832,527 is a step forward in the art and is particularly useful in conjunction with a feedhorn having a wide end with a substantially circular cross-section. If the wide end of the feedhorn has a differently shaped cross-section, such as a rectangular cross-section, it may be somewhat difficult to form the heater assembly to closely conform to the exterior periphery of the feedhorn, depending upon the radius of curvature between adjacent flat surfaces, etc.
What is needed in the art is a heater assembly to prevent or melt ice accumulation on a feedhorn and on the window covering the end of the feedhorn, regardless of the cross-sectional shape of the wide end of the feedhorn.